1. Field of the Invention
The present invention relates to a method of socketing a pipe of oriented plastic having an annular groove inside the socket. This groove is provided to receive an elastic gasket for sealing between the socket and a spigot end of another pipe when two pipes are to be interconnected.
2. Description of Related Art
The common method in forming a socket or bell on a pipe of plastic which is not oriented, and at the same time providing an annular groove inside the socket comprises heating of an end portion of the pipe to a temperature substantially above the glass transition temperature of amorphous plastic or the crystalline melting point of crystalline plastic, respectively, and pushing the heated end portion of the pipe onto a mandrel having a collapsible core for forming said groove. The core is in the expanded condition when the end portion is pushed onto the mandrel. After cooling of the end portion the core is collapsed and the socketed pipe is withdrawn from the mandrel.
It is also prior art to slip a sealing ring or gasket onto the mandrel and to form the groove in the end portion of the pipe over the sealing ring which is left in the groove and is withdrawn from the mandrel together with the pipe.
When the socket shall be formed on a pipe of oriented plastic, particularly of MOPVC (molecular oriented polyvinylchloride) two problems are encountered which do not exist in case of pipes of non-oriented plastics material, viz.
1) to avoid stress concentration in the plastic material during socketing in the region where the groove shall be formed (the material is more sensitive to cracking around the periphery than normally because draw normally is higher in the hoop direction than in the axial direction), and PA1 2) to control accurately the degree of possible axial shrinkage during socketing thus avoiding unnecessary compression that might reduce the elongation at break,
These problems are overcome by the method of the present invention.